3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
The 3GPP LTE may configure carrier aggregation (CA). In CA, two or more component carriers (CCs) are aggregated in order to support wider transmission bandwidths up to 100 MHz. A user equipment (UE) may simultaneously receive or transmit on one or multiple CCs depending on its capabilities.
Further, as the demands on data rate keeps increasing, the utilization/exploration on new spectrum and/or higher data rate is essential. As one of a promising candidate, utilizing unlicensed spectrum, such as 5 GHz unlicensed national information infrastructure (U-NII) radio band, is being considered. As it is unlicensed, to be successful, necessary channel acquisition and completion/collision handling and avoidance are expected. As LTE is designed based on the assumption that a UE can expect DL signals from the network at any given moment (i.e., exclusive use), LTE protocol needs to be tailored to be used in non-exclusive manner. In terms of non-exclusive manner, overall two approaches may be considered. One is to allocate time in a semi-static or static manner (for example, during day time, exclusive use, and during night time, not used by LTE), and the other is to compete dynamically for acquiring the channel. The reason for the completion is to handle other radio access technology (RAT) devices/networks and also other operator's LTE devices/networks.
By introduction of utilizing unlicensed spectrum, a new type of band utilization may be feasible. Specifically, an uplink (UL)-only spectrum may be used. In this case, a method for performing UL synchronization in the UL only spectrum may be a problem.